Installed on a Dell Dimension c521 (from 2006 or so). It may take a minute or an hour, but inevitably the mouse pointer will randomly stop responding. I've tried three different mice plugged into different USB ports but get the same thing. The machine previously ran Windows XP for five years without any such trouble.

I do not have the offending machine in front of me right now, but I plan to look for anything suspicious in the dmesg log. Where else and for what else should I look?

On today's systems, notebooks in particular (but not restricted to these), ACPI is mandatory for temperature control, in its absence there is a very real danger that the system overheats and gets physically damaged. That said, SMP also requires ACPI to enable CPU cores.